In disc drive systems, the discs are mounted on a hub of a spindle motor for rotation at an approximately constant high speed during the operation of the disc drive. An actuator assembly in the disc drive moves magnetic transducers, also called read/write heads, to various locations relative to the discs while the discs are rotating, and electrical circuitry is used to write data to and read data from the media through the read/write heads. The fly height, also called clearance, is a distance between the read/write head and the media.
Disc drives are being produced with increasing track densities and decreasing access times. A read/write head must fly over the media of a disc as closely as possible to improve reading and writing access times. Further, the fly height of the head should be approximately uniform from read mode to write mode and during the reading and writing to improve system performance.
Several variables can affect the fly height of a head. For example, fly height is impacted by a curvature of a disc, vibrations of the disc caused by the spindle motor, and roughness and defects in the media. Fly height is also affected by variation in the heat dissipated in the head due to the differential in the power characteristics of the head while in the read mode versus the write mode. For example, heat causes the read/write head to expand. As more power is delivered to the head, the head tends to expand more. Therefore, the head will tend to expand more during a reading or writing operation as the head heats up. The head will also expand more during the write mode since it requires more power to write than read. The disturbance decreases performance and/or increases the possibility of an error in reading from or writing to the media.
Several efforts have been made to improve control of the fly height of a read/write head. However, none of the efforts have resulted in a suitable solution to the aforementioned heat disturbance problem. There remains a need for a system to control the fly height of a read/write head to allow it to read data from or write data to closely spaced media.